Generally, in an image processing device such as a digital copying machine for treating image data, image data is read from an original document by image reading means such as a scanner, and digitized. The digital image data is processed in accordance with the purpose, multileveled, and output through image output means such as a laser printer. The image processing device has a density adjusting function. The density adjusting function automatically adjusts density of the print to be suitable for the original document, if the image data read by the scanner includes a background portion of the original document or the letters in the original document are light-colored.
The density adjusting function includes the following functions. First function generates a density histogram from an input image data. Second function determines the kind of the input original document, that is, the kind of the input image data on the basis of characteristic value of the generated density histogram. Third function corrects an image tone of the input image data in accordance with the determination result.
Japanese Unexamined Patent Application Publication No. H10-191059 discloses an image processing device. The image processing device has a function of removing a background. When removing a background, the image processing device selects a density correction table from a plurality of predetermined density correction tables on the basis of the determination result of the characteristics of the original document. The image processing device performs a process of removing the background on the basis of the selected density correction table.